Make image_decoder a Leaky LazyInstance

chrome/browser/image_decoder.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_IMAGE_DECODER_H_
 #define CHROME_BROWSER_IMAGE_DECODER_H_
 
+#include <map>
 #include <string>
 #include <vector>
 
 #include "base/compiler_specific.h"
+#include "base/id_map.h"
+#include "base/lazy_instance.h"
 #include "base/memory/ref_counted.h"
 #include "base/threading/sequenced_worker_pool.h"
+#include "base/timer/timer.h"
+#include "content/public/browser/utility_process_host.h"
 #include "content/public/browser/utility_process_host_client.h"
 
 class SkBitmap;
 
-// Decodes an image in a sandboxed process.
-class ImageDecoder : public content::UtilityProcessHostClient {
+// This is a helper class for decoding images safely in a utility process. To
+// use this, call ImageDecoder::GetInstance()->Start(...) on any thread.
+//
+// Internally, all of the work happens on the IO thread, and then
+// the result (Delegate::OnImageDecoded or Delegate::OnDecodeImageFailed) is
+// posted back to the task runner specified when Start(...) was called.
+class ImageDecoder {
  public:
   class Delegate {
    public:
     // Called when image is decoded.
-    // |decoder| is used to identify the image in case of decoding several
-    // images simultaneously.
-    virtual void OnImageDecoded(const ImageDecoder* decoder,
-                                const SkBitmap& decoded_image) = 0;
+    virtual void OnImageDecoded(const SkBitmap& decoded_image) = 0;
 
     // Called when decoding image failed. Delegate can do some cleanup in
     // this handler.
-    virtual void OnDecodeImageFailed(const ImageDecoder* decoder) {}
+    virtual void OnDecodeImageFailed() {}
 
    protected:
     virtual ~Delegate() {}
   };
 
   enum ImageCodec {
     DEFAULT_CODEC = 0,  // Uses WebKit image decoding (via WebImage).
     ROBUST_JPEG_CODEC,  // Restrict decoding to robust jpeg codec.
   };
 
-  ImageDecoder(Delegate* delegate,
-               const std::string& image_data,
-               ImageCodec image_codec);
-
-  ImageDecoder(Delegate* delegate,
-               const std::vector<char>& image_data,
-               ImageCodec image_codec);
+  static ImageDecoder* GetInstance();
 
   // Starts asynchronous image decoding. Once finished, the callback will be
   // posted back to |task_runner|.
-  void Start(scoped_refptr<base::SequencedTaskRunner> task_runner);
+  void Start(Delegate* delegate,
+             const std::string& image_data,
+             ImageCodec image_codec,
+             scoped_refptr<base::SequencedTaskRunner> task_runner,
+             bool shrink_to_fit);
 
-  const std::vector<unsigned char>& get_image_data() const {
-    return image_data_;
-  }
-
-  void set_delegate(Delegate* delegate) { delegate_ = delegate; }
-  void set_shrink_to_fit(bool shrink_to_fit) { shrink_to_fit_ = shrink_to_fit; }
+  // Removes all instances of delegate from the IDMap, ensuring callbacks
+  // are not made to the delegate after it is destroyed.
+  void RemoveDelegate(Delegate* delegate);
 
  private:
-  // It's a reference counted object, so destructor is private.
-  ~ImageDecoder() override;
+  friend struct base::DefaultLazyInstanceTraits<ImageDecoder>;
+  ImageDecoder();
+  ~ImageDecoder();
 
-  // Overidden from UtilityProcessHostClient:
-  bool OnMessageReceived(const IPC::Message& message) override;
+  class ImageDecoderImpl : public content::UtilityProcessHostClient {
+   public:
+    ImageDecoderImpl();
 
-  // IPC message handlers.
-  void OnDecodeImageSucceeded(const SkBitmap& decoded_image);
-  void OnDecodeImageFailed();
+    // Sends a request to the sandboxed process to decode the image. Starts
+    // batch mode if necessary.
+    void DecodeImageInSandbox(
+        Delegate* delegate,
+        const std::vector<unsigned char>& image_data,
+        ImageCodec image_codec,
+        scoped_refptr<base::SequencedTaskRunner> task_runner,
+        bool shrink_to_fit);
 
-  // Launches sandboxed process that will decode the image.
-  void DecodeImageInSandbox(const std::vector<unsigned char>& image_data);
+    void RemoveDelegate(Delegate* delegate);
 
-  Delegate* delegate_;
-  std::vector<unsigned char> image_data_;
-  const ImageCodec image_codec_;
-  scoped_refptr<base::SequencedTaskRunner> task_runner_;
-  bool shrink_to_fit_; // if needed for IPC msg size limit
+   private:
+    // It's a reference counted object, so destructor is private.
+    ~ImageDecoderImpl() override;
+
+    // Contains attributes we need to know about each image decode
+    // request we send.
+    struct RequestInfo {
+      RequestInfo(Delegate* delegate,
+                  scoped_refptr<base::SequencedTaskRunner> task_runner);
+      ~RequestInfo();
+
+      Delegate* delegate;
+      scoped_refptr<base::SequencedTaskRunner> task_runner;
+    };
+
+    // Starts UtilityProcessHost in batch mode and starts batch_mode_timer_.
+    void StartBatchMode();
+
+    // Stops batch mode if no requests have come in since kBatchModeTimeout.
+    void StopBatchMode();
+
+    // Overidden from UtilityProcessHostClient.
+    bool OnMessageReceived(const IPC::Message& message) override;
+
+    // IPC message handlers.
+    void OnDecodeImageSucceeded(const SkBitmap& decoded_image, int id);
+    void OnDecodeImageFailed(int id);
+
+    // id to use for the next Start request that comes in.
+    int delegate_id_counter_;
+
+    // Map of request id's to RequestInfo.
+    IDMap<RequestInfo> request_info_id_map_;
+
+    // The UtilityProcessHost requests are sent to.
+    base::WeakPtr<content::UtilityProcessHost> utility_process_host_;
+
+    // Calls StopBatchMode after kBatchModeTimeout has elapsed.
+    base::RepeatingTimer<ImageDecoderImpl> batch_mode_timer_;
+
+    // The time Start was last called.
+    base::TimeTicks last_request_;
+
+    // How long to wait after the last request has been received before ending
+    // batch mode.
+    const base::TimeDelta kBatchModeTimeout = base::TimeDelta::FromSeconds(5);
+
+    // True iff utility_process_host_ has been created and started in
+    // batch mode.
+    bool batch_mode_started_;
+  };
+
+  const scoped_refptr<ImageDecoderImpl> image_decoder_impl_;
 
   DISALLOW_COPY_AND_ASSIGN(ImageDecoder);
 };
 
 #endif  // CHROME_BROWSER_IMAGE_DECODER_H_